The present disclosure relates to copolymers and resin compositions containing the copolymers preferred as a material for a phase difference film of a liquid crystal display device or the like, a film and a phase difference film.
Many kinds of optical film are used to improve display characteristics of liquid crystal display devices. For example, in an IPS (In-Plane-Switching) mode, which applies a transverse electric field to liquid crystal, a method combining a phase difference film having negative birefringence, as an optical compensation film, between a liquid crystal layer and a polarizing plate has been proposed. The phase difference film is provided, as one of means for improving color tones and viewing angles at black state. Such a phase difference film is obtainable by stretching a resin having a negative value of intrinsic birefringence. For example, a negative phase difference film obtainable by forming a film from a resin having negative intrinsic birefringence, such as fumaric acid ester resin and aromatic acyl-substituted cellulose resin, and by stretching the film has been proposed (Japanese Patent No. 5387647 (hereinafter, also referred to as “Patent Document 1”) and Japanese Patent No. 5203066 (hereinafter, also referred to as “Patent Document 2”)).
Japanese Patent Laid-Open Publication No. 2006-036967 (hereinafter, also referred to as “Patent Document 3”) described the feature that a negative phase difference film having excellent heat resistance, transparency and mechanical characteristic is producible by using a resin composition of N-phenylmaleimide resin and styrene-based copolymer mixed together, that is, a blend polymer of N-phenylmaleimide resin and styrene-based copolymer.